System for minimizing the impact of poisoning of automotive exhaust aftertreatment systems

ABSTRACT

An exhaust aftertreatment system for an internal combustion engine is disclosed which mitigates deleterious poisoning of a catalytic converter or exhaust gas oxygen sensor by phosphorus containing species.

RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.10/063,285, filed 8-Apr.-2002 now U.S. Pat. No. 6,810,660.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates generally to a system for minimizing thedeleterious impact of oil-derived phosphorus containing compounds onautomotive exhaust aftertreatment systems.

2. Background of the Invention

Automotive oils typically contain a zinc dialkyldithiophosphate (ZDDP)additive which forms an antiwear coating on engine components and actsas an antioxidant in the oil. Although engines are designed to minimizethe quantity of engine oil exiting the engine via the combustion chamberand exhaust system, it is inevitable that a small fraction of engine oilis released by this mechanism. The ZDDP additive of engine oildeleteriously affects catalytic converters due to phosphorus from theZDDP interfering with active sites within the catalyst. These phosphoruscontaining species deposit onto, or react with washcoat components, suchas aluminum oxide and cerium oxide, and remain there indefinitely. Thisphenomenon is commonly referred to as phosphorus poisoning.

Measures to eliminate or reduce ZDDP in engine oils have beeninvestigated. Alternatives to ZDDP have been produced which have beenshown to provide antioxidant and antiwear properties similar to ZDDP.However, they are cost prohibitive. Engine oils may be formulated with alesser amount of ZDDP with the consequences that engine wear and oiloxidation increase, the former limiting engine life and the latterreducing useful oil life.

The inventor of U.S. Pat. No. 5,857,326 has disclosed an exhaust poisontrap which comprises a helical wall dividing the exhaust chamber intolongitudinal helical passages for exhaust gas flow and porous meanscovering the interior of the peripheral wall. The inventor of '326teaches that exhaust gas is directed in a helical path causingparticulate matter in the gas to be accelerated outwardly by centrifugalforce and trapped in the porous means. The inventor of the presentinvention has recognized several limitations of the approach in '326.The helical passages cause the exhaust gases to be rotated and particlesthat have a diameter less than a certain size follow the flow and avoidbeing trapped in the porous means near the walls of the tube and largerparticles impact the porous means near the walls. The device disclosedin '326 has the capability of causing only the largest particles to beremoved. The figures in '326 indicate that the helical wall causes theflow to rotate through at least two revolutions and as many as fourrevolutions. The length of the exhaust poison trap is approximately twoto four pipe diameters long with the disadvantages of complicating thepackaging of the exhaust poison trap and increasing the weight of thetrap, the thermal mass of which interferes with the desire to bring thecatalytic converter to its operating temperature as soon as possibleafter starting the engine to control cold start emissions.

SUMMARY OF INVENTION

Disadvantages of prior art are overcome by an exhaust aftertreatmentsystem for a spark-ignition, reciprocating internal combustion enginehaving a catalytic converter in an exhaust duct of the engine whichreceives an exhaust gas stream from the engine. The system comprises atrap in the exhaust duct located upstream of the catalytic converter.The trap is made of a porous ceramic or metallic material having anaverage pore size greater than about 80 micrometers. The porous materialsubstantially fills the cross-section of the exhaust duct and has avolume of than 10% of a swept volume of the engine's cylinders coupledto the trap. Exhaust gases undergo multiple, random turns in travelingfrom an upstream side to a downstream side of the trap. The trap islocated within 15 centimeters of the catalytic converter. An exhaust gascomponent sensor is placed downstream of the phosphorus trap.

Also disclosed is an exhaust aftertreatment system for processingexhaust gases from a reciprocating internal combustion engine, whichincludes a catalytic converter disposed in an exhaust duct of theengine. The catalytic converter has channels for conducting exhaustgases from an upstream end to a downstream end. The channels aresubstantially parallel to each other and parallel to a direction of flowthrough the catalytic converter. The catalytic converter has a ceramicor metallic porous material disposed within the channels from theupstream end of the catalytic converter for a predetermined distancealong the catalytic converter. The porous material has randomly orientedpassageways causing the exhaust gases to undergo multiple turns in thecourse of being transmitted through the porous material.

Also disclosed is an exhaust aftertreatment system for a reciprocatinginternal combustion engine comprising a phosphorus trap in an exhaustduct of the engine made of a porous material and substantially fillingthe cross-section of the exhaust duct. The porous material has anaverage pore size greater than a predetermined pore size and hasrandomly oriented passageways forcing exhaust gases passing through toundergo multiple turns. The system also has a catalytic converterdisposed in the exhaust duct of the engine located downstream of thephosphorus trap and an electronic control unit operably connected to theengine. The electronic control unit provides an indication of an amountof phosphorous containing material trapped in the phosphorus trap andraises temperature in the phosphorous trap above a predeterminedtemperature when the amount of phosphorous containing material exceeds apredetermined quantity. The indication is based on time of operation ora value of an engine parameter since the predetermined temperature hasbeen achieved.

A primary advantage of the present invention is that phosphoruscontamination of the exhaust aftertreatment system can be decreased byapproximately 60% in the absence of taking other preventative measures,which are costly. Reduced phosphorus contamination, as provided by thepresent invention, allows the catalyst to operate at high conversionefficiency over the life of the vehicle.

The inventors of the present invention have recognized that theeffectiveness of the phosphorus trap is improved if it operates at atemperature close to the temperature of the catalytic converter. Thus,another advantage of the present invention is higher capture efficiencyof deleterious phosphorus containing particles by placing the phosphorustrap in close proximity to the catalytic converter.

Another advantage of the present invention is that it removes particlesof smaller diameter than prior approaches and does so with a negliblepressure drop across the phosphorus trap.

Yet another advantage of the present invention is that vehicles withunusual driving patterns may be operated in such a way to allow suchvehicles to also benefit from the present invention.

The present invention may also be used to advantage combined with quickwarmup strategies such as cold start spark retard and exhaust portoxidation.

The inventors of the present invention have recognized that thephosphorus trap may be much smaller than in prior approaches. Thesmaller size affects the warmup time of the exhaust system less thanlarger traps, a decided advantage in preventing cold start emissions.

Another advantage of the present invention is that, if the phosphorustrap is placed upstream of an exhaust gas oxygen sensor or other exhaustcomponent sensor, deterioration of the sensor is prevented or slowed.

Without a phosphorus trap located upstream of a catalytic converter, theconverter volume is chosen which provides sufficient conversion capacityover the targeted lifetime. An advantage of the present invention isthat the volume can be reduced because the phosphorus trap protects thecatalytic converter from phosphorus poisoning.

Yet another advantage is that, if the phosphorus trap is coated with awashcoat, it can provide some additional conversion capability,particularly during cold start.

The above advantages, other advantages, and features of the presentinvention will be readily apparent from the following detaileddescription of the preferred embodiments when taken in connection withthe accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment in which the invention is used to advantage,referred to herein as the Detailed Description, with reference to thedrawings wherein:

FIG. 1 is a schematic of an engine equipped with a phosphorous trapaccording to an aspect of the present invention;

FIG. 2 shows a portion of a cross-section of a catalytic converter witha phosphorus trap integrated into the channels of the catalyticconverter according to an aspect of the present invention;

FIG. 3 shows a representative structure of a phosphorus trap;

FIG. 4 is a flowchart of a method for operating an internal combustionengine according to an aspect of the present invention; and

FIG. 5 is a flowchart of a method for operating an internal combustionengine according to an aspect of the present invention.

DETAILED DESCRIPTION

An engine 10 equipped with a phosphorous trap 30 according to an aspectof the present invention is shown in FIG. 1. Engine 10 is supplied airthrough intake manifold 12 past throttle valve 14 and is supplied fuelthrough fuel injectors 16 spraying fuel into intake manifold 12. Theconfiguration shown in FIG. 1 is commonly referred to as port fuelinjection. The present invention also applies to direct fuel injection,in which fuel injectors 16 are installed directly in cylinders 32,central fuel injection, in which a single fuel injector 16 is placed inintake manifold 12 closer upstream of where intake manifold 12 separatesinto individual runners supplying individual cylinders 32, carburetion,and other fuel supplying devices. Ignition is provided by spark plugs18. The exhaust gases are expelled through exhaust manifold 28, intophosphorus trap 30, into catalytic converter 26, and exhausted to theatmosphere. Sensor 24 is an exhaust gas component sensor, preferably anexhaust gas oxygen sensor. Alternatively, sensor 24 is a NOx sensor, HCsensor, CO sensor, or other component sensor.

ECU 40 is provided to control engine 10 as shown in FIG. 1. ECU 40 has amicroprocessor 72, called a central processing unit (CPU), incommunication with memory management unit (MMU) 74. MMU 74 controls themovement of data among the various computer readable storage media andcommunicates data to and from CPU 72. The computer readable storagemedia preferably include volatile and nonvolatile storage in read-onlymemory (ROM) 76, random-access memory (RAM) 80, and keep-alive memory(KAM) 78, for example. KAM 78 is used to store various operatingvariables while CPU 72 is powered down. The computer-readable storagemedia may be implemented using any of a number of known memory devicessuch as PROMs (programmable read-only memory), EPROMs (electricallyPROM), EEPROMs (electrically erasable PROM), flash memory, or any otherelectric, magnetic, optical, or combination memory devices capable ofstoring data, some of which represent executable instructions, used byCPU 72 in controlling the engine or vehicle into which the engine ismounted. The computer-readable storage media may also include floppydisks, CD-ROMs, hard disks, and the like. CPU 72 communicates withvarious sensors and actuators via an input/output (I/O) interface 70.Examples of items that are actuated under control by CPU 72, through I/Ointerface 70, are fuel injection timing, fuel injection rate, fuelinjection duration, throttle valve 14 position, spark plug 18 timing,and others. Sensors 42 communicating input through I/O interface 70 maybe indicating engine rotational speed, vehicle speed, coolanttemperature, intake manifold 12 pressure, pedal position, throttle valve14 position, air temperature, exhaust temperature, and air flow. SomeECU 40 architectures do not contain MMU 74. If no MMU 74 is employed,CPU 72 manages data and connects directly to ROM 76, RAM 80, and KAM 78.The present invention could utilize more than one CPU 72 to provideengine control and ECU 40 may contain multiple ROM 76, RAM 80, and KAM78 coupled to MMU 74 or CPU 74 depending upon the particularapplication.

Catalytic converter 26 is commonly called a three-way catalyst which canprocess NOx, hydrocarbons, and CO, although the invention canpotentially be used with a wide variety of catalyst systems includingthose for lean-burn engines, diesel engines, and various alternativelyfueled vehicles among others. Although only one converter is shown inFIG. 1, it should be appreciated that most vehicles contain multiplecatalyst elements, sometimes in the same converter housing and sometimesin separate converters. V engines often contain separate catalyticconverters coupled to each engine bank of engine cylinders. In addition,typical converter systems consist of a catalyst mounted close to theengine (light-off converter) and one or more converters locateddownstream in either so-called to-board or underbody positions. In thepresent invention, the converter of greatest inters is the light-offconverter because this is the one in which the majority of the poisonspecies are captured.

Typical three-way catalysts are comprised of extruded ceramic ormetallic material forming a myriad of parallel passageways of about 1millimeter in hydraulic diameter. The extruded substrate is treated toprovide precious metals on the surface of the passageways through thesubstrate via high-surface-area washcoat components such as aluminumoxide, cerium oxide, and zirconium oxide. In particular, the cerium andzirconium oxide materials, and combinations of the two, constituteoxygen storing species which improve the efficacy of the conversionprocess. When these oxygen storage sites are occupied by phosphoruscontaining compounds, the number of oxygen storage sites that can beused for aiding in converting CO, NOx, and hydrocarbons is decreased.Alternatively, phosphorus species can react with aluminum oxide to formaluminum phosphate, thereby causing densification of the washcoatstructure, pore blocking, and occlusion of active noble metals. Yetanother mechanism by which phosphorus species can interfere withcatalyst effectiveness is through the formation of an overlayer on thesurface of the washcoat. This overlayer generally consists of variousphosphate compounds of zinc, calcium, and magnesium, and can impede thediffusion of the reactive gases from the bulk gas stream to the activesites within the washcoat layer. If phosphorus contamination continues,in time, the effectiveness of catalytic converter 26 is seriouslyimpaired.

In FIG. 1, catalytic converter 26 is shown separated from phosphorustrap 30 and exhaust gas oxygen sensor 24 is placed downstream ofphosphorus trap 30. Like catalytic converter 26, exhaust gas oxygensensor 24 is treated with precious metals bonded onto its surface tocatalyze the reaction of CO, NOx, and hydrocarbons. Exhaust gas oxygensensor 24 is also harmed by contamination by phosphorus containingspecies. Thus, an advantage of the configuration shown in FIG. 1 is thatexhaust gas oxygen sensor 24 is protected from deterioration byphosphorus species.

Alternatively, phosphorus trap 30 is placed within the catalyticconverter 26 housing at the upstream end of catalytic converter 26(configuration not shown). In this configuration, exhaust gas oxygensensor 24 is located upstream of both catalytic converter 26 andphosphorus trap 30 and is not protected from phosphorus contamination.

Referring now to FIG. 2, another alternative configuration is shown. Asdescribed above, catalytic converter 26 contains many parallelpassageways along its length, as shown in FIG. 2. According to an aspectof the present invention, the porous material, of which phosphorus trap30 is comprised, is inserted into the upstream end of the passageways.

The inventors of the present invention have recognized that unburned orpartially oxidized engine oil containing ZDDP additive, condenses in theexhaust gas when the temperature is lower than about 200° C. Suchcondensable material is captured by the catalytic converter with highefficiency unlike more fully oxidized phosphorus containing specieswhich exist in the vapor form and have greater likelihood of passingthrough the catalytic converter without being captured. The mechanism,by which catalytic converter 26 is harmed, is that the unburned orpartially oxidized phosphorus containing species condense on thesurfaces of catalytic converter 26. Catalytic converter 26 containshigh-surface-area components such as aluminum oxide and cerium oxide, onthe surface. Unoxidized and partially oxidized phosphorus species(arising from ZDDP additive in the oil) adsorb onto these components. Itis believed that the phosphorus species and the washcoat components formchemical bonds. Based on the present day state of the art, no in situ,cost effective measure of breaking those chemical bonds has beendetermined. Thus, oxygen storage sites that have been contaminated byphosphorus compounds are essentially unrecoverable, i.e., they are nolonger able to participate in catalytic reactions.

The inventors of the present invention have performed laboratoryexperiments showing contamination or capture efficiency of the partiallyoxidized or unoxidized phosphorus species of at least 50% and possiblyup to nearly 100% in catalytic converter 26.

When exhaust temperature exceeds about 400-500° C., partially oxidizedor unoxidized phosphorus species largely react to form fully oxidizedphosphates or species, which are more oxidized, such as phosphoric acid,phosphorus pentoxide, and a dimer of phosphorus pentoxide. These speciesare vapor phase, even at temperatures below 200-250° C. These species donot normally condense until the exhaust gas temperature falls to levelsbelow 80-100° C. where condensation occurs along with condensation ofwater from the exhaust gases. The inventors of the present inventionhave found that the capture efficiency of these vapor phase phosphoruscompounds and the phosphate related particulates (eg., zinc phosphate)is less than about 20% in catalytic converter 26 and the phosphates arelargely benign. Thus, the inventors of the present invention haverecognized that if harmful condensable phosphorus species can beprevented from entering the catalytic converter when the temperature isless than 200-250° C., when the exhaust system subsequently achieves atemperature exceeding 400° C., harmful condensable phosphorus speciesreact into the less harmful vapor species or to the nearly harmlessphosphates. The probability of the phosphorus materials poisoningcatalyst 26 reduces from 50% to 20% if reacted to the vapor species orto much less than 20% if reacted to phosphates. The poisoning risk tocatalyst 26 is reduced by more than 60%. The oxidation temperature forthe phosphorus species is in the range of 200-250° C. Below, thetemperature 225° C. is used to indicate this range.

In engines equipped with three-way, oxygen-storing catalytic convertersexhaust temperatures are below 225° C. only during cold start andextended idle periods. Thus, if condensable phosphorus species arecollected in trap 30 prior to entering catalyst 26, these condensablephosphorus species convert to less harmful species when the temperaturein trap 30 rises above 225° C. Thus, the trap regenerates spontaneouslywhen exhaust temperature achieves normal operating temperature. Theinventors of the present invention have recognized that only a smallamount of the condensable phase phosphorus species is generated by theengine during any such operating interval with low exhaust temperatures,except for unusual operating patterns and thus, the desired volume oftrap 30 capable of capturing the emitted material is small. On anexceptional basis, exhaust temperatures may remain low under unusualoperating cycles, which is discussed in more detail below. The smallsize and mass of trap 30, according to the present invention, overcomesthe disadvantage of traps with large thermal inertia of priorapproaches. Trap 30 is constructed of ceramic or metallic foam of poresize roughly 100 micrometers and a minimum pore size of 20 micrometers.Alternatively, trap 30 may be constructed of other porous materials,which provide pore sizes as mentioned above, random passages therethrough, and can withstand the temperatures encountered in the exhaustduct. Unlike catalytic converter 26, which has parallel passagewaysthrough which the exhaust gases pass, trap 30 has random passagewayscausing the exhaust gases to twist and turn to pass through trap 30. Itis the inability of the droplets and aerosol particles to negotiateturns in trap 30 that causes them to impact onto the foam materialitself. The inventors of the present invention have recognized that thevolume of trap 30 is less than about 10% of the swept volume (ordisplacement) of engine 10. Swept volume is found by multiplying thecross-sectional area of a piston times the travel distance of the pistonduring a single stroke times the number of cylinders in engine 10.

Trap 30 can be coated with a washcoat similar to that used in athree-way catalyst. Trap 30 would be beneficial in reducing tailpipeemissions during cold start, i.e., prior to when catalyst 26 has reachedoperating temperature. The washcoat of trap 30 would become poisonedover time and its ability to provide conversion hampered. Nevertheless,during the time that trap 30 is fresh, cold start emissions would bereduced.

If engine 10 is a multi-bank engine, eg. V-8, in which catalysts aredisposed in exhaust ducts coming from each bank of the engine,preferably a phosphorus trap 30 is placed in each exhaust duct upstreamof the catalyst. In this case, the volume of phosphorus trap 30 isrelated to the displaced volume of the cylinders to which it is coupled.Each trap 30 is comprised, preferably, of a single, integral structurerequiring little external support, except for being held in place at theperiphery. This is in contrast to a pellet-type trap comprised ofnumerous pellets which must be retained within a container.

It is known in the art to use a diesel particulate filter (DPF) to trapcarbonaceous particles exhausted from a diesel engine. DPFs are designedsuch that they collect greater than 90% of all particles. To be able tocollect the smallest particles (as small as several nanometers), theaverage pore size of a DPF is typically about 20 micrometers and a DPFhas a volume roughly equal to 1-3 times the engine's displacementvolume. Because of the DPF's small pore size and large volume, a DPFprovides considerable resistance to exhaust gas flow, roughly 25 kPawhen the trap is empty and roughly 50 kPa when the trap is full (thesepressure drops occur at an engine condition generating peak enginepower, i.e., when flow through the exhaust system is at highest).Typical DPFs are constructed of parallel channels along the direction offlow through the DPF. Every other channel is blocked on the upstreamend. On the downstream end of the DPF those channels, which areunblocked on the upstream end, are blocked on the downstream end. Thisforces exhaust gases to traverse through channel walls. This has beenfound to allow high collection efficiency over a wide range of particlesizes.

In contrast, the desire is for phosphorus trap 30 to collect onlyparticles greater than about several micrometers in diameter and allowthe passage of smaller particles. The inventors of the present inventionhave recognized that it is preferable to allow smaller particles totravel through trap 30 without being trapped because smaller particlespermanently lodged in trap 30 ultimately occludes the trap, causing asignificant pressure drop. According to the present invention,phosphorus trap 30 has an average pore size of at least 50 micrometerswith a minimum pore size of greater than about 20 micrometers. For thepurposes of the present invention, trap 30 need only be about 10% ofengine displaced volume, if the trap is made of metallic foam, and about15% of engine displacement volume, if the trap is made of ceramic foam.Because of the relatively large pore size and small volume of trap 30,the pressure drop across trap 30 is negligible, less than about 1 kPa.

Typically, DPFs have a porosity of about 50%; whereas, the phosphorustrap 30, of the present invention, has a porosity greater than about90%. Because of the high porosity and small volume of phosphorus trap30, for a typical automotive engine, the mass of the porous material inphosphorus trap 30 is roughly 50 to 200 g depending on the material oftrap 30. It is expected that the mass of phosphorus trap 30 be relatedto displacement of the cylinders to which trap 30 is coupled, eg., mass(in grams) of trap 30 is less than roughly engine displacement (in cubiccentimeters) divided by 25. The length of trap 30 is about one-third ofthe diameter of the exhaust duct in which it is contained.

In the preceding discussion, collection characteristics of a DPF and aphosphorus trap 30 are compared. It was stated that phosphorus trap 30collects particles above one micrometer in diameter. It is known,however, to those skilled in the art, that filters of the typesdiscussed do not have sharp cutoffs in the size of particles collected.Thus, phosphorus trap 30, even though designed to collect particlesgreater in diameter than one micrometer, collects particles smaller thanone micrometer, but at low efficiency. Furthermore, the collectionefficiency, as a function of particle diameter, is affected by thevelocity of the gases at the face of the filter or trap. Thus, thenumbers given above are representative, but not limiting. Also, thespecific characteristics of phosphorus trap 30 are given by way ofexample and are not intended to be limiting.

An example of the structure of phosphorus trap 30 is shown in FIG. 3.FIG. 3 is a drawing based on a photomicrograph of the face of a metallicfoam suitable for use as phosphorus trap 30. The magnification in thedrawing is roughly 100×. The smaller pores, in FIG. 3, that aresignificantly smaller than the expected 100 micrometers are due to thembeing pores which are slightly below the surface, and thus partiallyoccluded from view by portions of upper pores. It can be seen in FIG. 3that the material is irregular causing gases to twist and turn randomlyin passing through phosphorus trap 30.

As mentioned above, some vehicles with unusual operating patterns mayoperate for extended periods with the exhaust temperature less than 225°C. As example is a taxicab, which may idle for extended intervals. Theinventors of the present invention have recognized that phosphorus trap30 is purged of condensable phase phosphorus species if the temperatureis raised above 225° C. for a short period. According to the presentinvention, it is determined when trap 30 can no longer retain moredroplets containing condensable phase phosphorus species. When thatdetermination is made, engine 10 operation is changed to cause thetemperature in the exhaust to exceed 225° C.

The method of purging phosphorus trap 30, according to an aspect of thepresent invention, is shown in FIG. 4. A phosphorus trap purge routinebegins in step 100 when engine 10 is started. In step 102, RAM 80 memorylocation, t, is filled with the contents of a KAM 78 memory location,t_(resid), which is the operating time elapsed since the last purge oftrap 30. As engine 10 has just been started, the value of t_(resid) isbased on a prior operating interval of engine 10. In step 104, it isdetermined whether the temperature in trap 30, T_(Ptrap), greater than athreshold temperature, T_(thresh). T_(thresh) is the temperature atwhich condensable phase phosphorus compounds oxidize to form lessharmful phosphorus species. If step 104 yields a positive result,control passes to step 116, where t is reset to 0, which means that trap30 is purged of condensable phase phosphorus species. In normal, warmedup operation, the routine of FIG. 4 cycles between steps 116 and 104.However, during unusual operating patterns and until engine 10 is warmedup, a negative result from step 104 occurs. Control then passes to step106 in which memory location t is incremented by the time elapsed sincethe last time t was updated, Δt. In step 108, t is compared tot_(thresh), which is a threshold time for which trap 30 has beenoperating long enough since the last purge to be substantially full. Ifa negative result from step 108, control passes back to step 104. If apositive result in step 108, control passes to step 110 where operatingconditions of engine 10 are altered to cause T_(Ptrap) to exceedT_(thresh). Control passes to step 112 where a check whether trap 30 hashad sufficient time to oxidize the condensable phase phosphorus species.If a negative result, engine 10 is maintained at the operating conditionto keep T_(Ptrap) above T_(thresh). When a positive results from step112, control passes to step 114 in which engine 10 is returned to normaloperating conditions. Control passes to step 116 in which t is reset to0. Also shown in FIG. 4 is an interrupt, step 120, which is when engine10 is shut off. The routine of steps 100-116 is diverted to step 120,when the interrupt is received. Control passes to step 122, in which thecurrent value of t is stored in t_(resid), the latter of which is in KAM78. The routine is ended in step 124.

The routine discussed in regard to FIG. 4 is based on a time ofoperation since the last purge. An alternative is to model the amount ofcondensable phase phosphorus material that is released. The model couldbe based on engine speed, other engine operating parameters, which areknown in ECU 40, or a combination of such parameters. Such a routine isshown in FIG. 5. The routine of FIG. 5 is identical to the routine ofFIG. 4, except that rather than basing the purge on a time of operation,the purge is based on a modeled mass of condensable phase phosphorusspecies, m, in trap 30.

The method of purging phosphorus trap 30, according to an aspect of thepresent invention, is shown in FIG. 5. A phosphorus trap purge routinebegins in step 200 when engine 10 is started. In step 202, RAM 80 memorylocation, m, is filled with the contents of a KAM 78 memory location,m_(resid), which is the time elapsed since the last purge of trap 30. Asengine 10 has just been started, the value of m_(resid) is based on aprior operating interval of engine 10. In step 204, it is determinedwhether the temperature in trap 30, T_(Ptrap), is greater than athreshold temperature, T_(thresh). T_(thresh) is the temperature atwhich condensable phase phosphorus compounds oxidize to form lessharmful phosphorus species. If step 204 yields a positive result,control passes to step 216, where m is reset to 0, which means that trap30 is purged of condensable phase phosphorus species. In normal, warmedup operation, the routine of FIG. 4 cycles between steps 216 and 204.However, during unusual operating patterns and until engine 10 is warmedup, a negative result from step 204 occurs. Control then passes to step206 in which memory location t is incremented by the time elapsed sincethe last time t was updated, Δt. In step 208, t is compared tot_(thresh), which is a threshold time for which trap 30 has beenoperating long enough since the last purge to be substantially full. Ifa negative result from step 208, control passes back to step 204. If apositive result in step 208, control passes to step 210 where operatingconditions of engine 10 are altered to cause T_(Ptrap) to exceedT_(thresh). Control passes to step 212 where a check whether trap 30 hashad sufficient time to oxidize the condensable phase phosphorus species.If a negative result, engine 10 is maintained at the operating conditionto keep T_(Ptrap) above T_(thresh). When a positive results from step212, control passes to step 214 in which engine 10 is returned to normaloperating conditions. Control passes to step 216 in which m is reset to0. Also shown in FIG. 4 is an interrupt, step 220, which is when engine10 is shut off. The routine of steps 200-216 is diverted to step 220,when the interrupt is received. Control passes to step 222, in which thecurrent value of m is stored in m_(resid), the latter of which is storedin KAM 78. The routine is ended in step 224.

To cause the temperature of the exhaust to rise, as discussed in regardsto step 110 of FIG. 4 and step 210 of FIG. 5, one or more of thefollowing measures may be undertaken: retarding the spark timing forsome or all cylinders, providing air and fuel to the exhaust such as byoperating some cylinders rich and others lean or by introducingsecondary air into the exhaust, loading engine 10 by causing thealternator to generate electricity for storage in the battery, loadingengine 10 with a power consuming accessory such as air conditioning,reducing cooling water flow rate to engine 10, turning off an enginecooling fan, raising engine speed, reducing exhaust gas recirculation,changing valve timing in engines equipped with variable valve timingmechanisms, and raising the temperature of the intake air.

While several modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize alternative designs and embodiments for practicing theinvention. The above-described embodiments are intended to beillustrative of the invention, which may be modified within the scope ofthe following claims.

1. An exhaust aftertreatment system for a reciprocating internalcombustion engine having at least one cylinder and a catalytic converterdisposed in an exhaust duct of the engine which receives an exhaust gasstream from the engine, comprising a trap disposed in the exhaust ductlocated upstream of the catalytic converter, said trap is comprised of aporous ceramic or metallic material having a predetermined average poresize, said trap substantially fills the cross-section of the exhaustduct, said trap having a porosity greater than 90% wherein exhaust gasesundergo multiple, random turns in traveling from an upstream side to adownstream side of said trap.
 2. The exhaust aftertreatment system ofclaim 1, said average pore size is greater than about 80 micrometers. 3.The exhaust aftertreatment system of claim 1, said trap is capable ofcollecting more than 90% of particles greater than 50 micrometers indiameter.
 4. The exhaust aftertreatment system of claim 1, said trapallows more than 50% of particles less than 1 micrometer in diameter topass through.
 5. The exhaust aftertreatment system of claim 1, saidporous material is foam.
 6. The exhaust aftertreatment system of claim1, a pressure drop across said phosphorus trap is less than onekilopascal.
 7. The exhaust aftertreatment system of claim 1 wherein saidtrap is located within 15 centimeters from an upstream end of thecatalytic converter.
 8. The exhaust aftertreatment system of claim 1, avolume of said trap is less than 10% of the swept volume of the engine'scylinders coupled to said trap.
 9. The exhaust aftertreatment system ofclaim 1, wherein said trap is treated with a washcoat capable ofcatalyzing oxidation reactions of carbon monoxide and hydrocarbons insaid exhaust gases.
 10. An exhaust aftertreatment system for an internalcombustion engine having at least one cylinder and a catalytic converterdisposed in an exhaust duct of the engine which receives exhaust gasstream from the engine comprising: a trap disposed in the exhaust ductlocated upstream of the catalytic converter, said trap is comprised ofchannels through which the exhaust gas stream flows, said channels beingirregular in cross-section wherein a trajectory of a centerline of saidchannels is random from an upstream face of said trap to a downstreamface of said trap.
 11. The exhaust aftertreatment system of claim 10,further comprising an exhaust gas component sensor disposed in theexhaust duct, said exhaust gas component sensor is located downstream ofsaid trap to protect said sensor.
 12. The exhaust aftertreatment systemof claim 10, wherein said trap is treated with a washcoat capable ofcatalyzing oxidation reactions of carbon monoxide and hydrocarbons insaid exhaust gases.
 13. An exhaust aftertreatment system for amulti-cylinder, reciprocating internal combustion engine having acatalytic converter disposed in an exhaust duct of the engine,comprising a trap disposed in the exhaust duct located upstream of thecatalytic converter, said trap is comprised of a metallic or ceramicporous material substantially filling the cross-section of the exhaustduct with randomly oriented passages through said porous material, apressure difference between an upstream side and a downstream side ofsaid phosphorus trap is less than1 kilopascal under all engine operatingconditions.
 14. The exhaust aftertreatment system of claim 13, said traphas a volume less than 10% of the swept volume of the cylinders coupledto said trap.
 15. The exhaust aftertreatment system of claim 13, saidporous material has a minimum pore size of about 20 micrometers.
 16. Theexhaust aftertreatment system of claim 13, said porous material has anaverage pore size of greater than about 80 micrometers.
 17. The exhaustaftertreatment system of claim 13 wherein a pressure drop across saidtrap is less than 1 kilopascal.
 18. The exhaust aftertreatment system ofclaim 13 wherein the catalytic converter is located within 15centimeters of said trap.
 19. An exhaust aftertreatment system for aninternal combustion engine having at least one cylinder and a catalyticconverter disposed in an exhaust duct of the engine which receives anexhaust gas stream from the engine, comprising: a trap disposed in theexhaust duct located upstream of the catalytic converter, said trapcomprising a porous metallic or ceramic foam material having a pluralityof irregularly shaped passages, walls of such passageways being providedby the foam material such walls being substantially thinner than suchpassageways.
 20. The system of claim 19 wherein the material is greaterthan 90% porous.
 21. The system of claim 19, said material is a foamwith pore size greater than 20 micrometers and average pore size greaterthan 80 micrometers.
 22. An exhaust aftertreatment system for aninternal combustion engine having at least one cylinder and a catalyticconverter disposed in an exhaust duct of the engine which receives anexhaust gas stream from the engine, comprising: a trap disposed in theexhaust duct located upstream of the catalytic converter, said trapcomprising a porous metallic or ceramic material having a plurality ofirregularly shaped passages, walls of such passageways being provided bythe material, wherein said material is a foam with pore size greaterthan 20 micrometers and average pore size greater than 80 micrometers.23. The system of claim 22 wherein such walls being substantiallythinner than such passageways.
 24. The system of claim 22 wherein thematerial is greater than 90% porous.
 25. An exhaust aftertreatmentsystem for a reciprocating internal combustion engine having at leastone cylinder and a catalytic converter disposed in an exhaust duct ofthe engine which receives an exhaust gas stream from the engine,comprising a trap disposed in the exhaust duct located upstream of thecatalytic converter, said trap is comprised of a porous ceramic ormetallic foam material forming channels irregular in cross-sectionwherein a trajectory of a centerline of said channels is random from anupstream face of said trap to a downstream face of said trap.